IEC 61920:2004 describes the classification of IR devices into groups and classes in order to identify and clarify problems caused by mutual interference. Mutual interference is caused by the increasing parallel application of different infrared (IR) systems. The wavelength range from 700 nm to 1 600 nm is considered. All systems based on free air application which intentionally or unintentionally use IR radiation in this range, are included. This second edition cancels and replaces the first edition published in 1998 and constitutes a technical revision. This bilingual version (2012-08) corresponds to the monolingual English version, published in 2004-01.